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Broker will start Authorizer plugins with AuthorizerServerInfo containing the new method 'Metrics metrics()' which has default implementation. Old version of Authorizer plugins will not call  the new method, so it is backward to old version of Authorizer plugins.    

Test Plan

Rejected Alternatives

Authorizer plugins create and configure own Metrics and JmxReport. Using this alternative approach make collecting Kafka metrics in Authorizer plugin separate from broker metrics that cause disconnection. Users need implement and manage own Metrics and JmsReport with extra effort. 

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